In chromatographic systems of the prior art, a single sample to be separated wastefully occupied only a small portion of a chromatographic column. A second sample was not introduced into such column until the first sample had been completely eluted. Accordingly, chromatographic separation of samples was an inefficient and time-consuming procedure. The present invention contemplates a much more efficient use of a chromatographic column. This increased efficiency is achieved by initially separating each of a number of samples fed seriatim into a first column into its individual components on a coarse basis. The eluant passing from the first column is sampled, so as to pass particular fractions of each sample seriatim through a second column, wherein a complete separation of the constituents is effected. This technique provides a passage of many sample fractions through the system concurrently. The over-all result is a dramatic increase in the throughput of the chromatographic system.